Analog amplifier cross vent



Oct. 18, 1966 D. R. JONES 3,279,488

ANALOG AMPLIFIER CROSS VENT Filed June 7, 1963 INVENTOR. 0. /0Lmv0do/vEs United States Patent 3,279,488 ANALOG AMPLIFIER CROSS VENT DonnieRoland Jones, Silver Spring, Md., assignor to Bowles EngineeringCorporation, Silver Spring, Md., a corporation of Maryland Filed June 7,1963, Ser. No. 286,309 Claims. (Cl. 137--81.5)

The present invention relates to pure fluid amplifiers and moreparticularly to an analog amplifier having a cross vent in theinteraction region to reduce noise and increase the gain of the unitover that which is realized when a cross vent is not employed.

Pure fluid amplifiers of the type with which the present invention isconcerned are a relatively recent development in the fluids field. Inthese devices amplification of an input signal is effected by producingan interaction between a so-called power stream of fluid and a controlsignal to deflect the jet in such a manner as to vary the proportions offluid received or applied to two or more downstream receiving or outputpassages. Deflection of the jet may be effected by momentum interchangebetween the power jet and one or more control streams of fluid, theinteraction between the two or more streams taking place in a regionwhere the power stream is confined to its plane of deflection. Inconsequence of the confinement of the power and control streams, amomentum interchange occurs between the control stream and the powerstream since the two streams cannot flow around one another but arerequired to impact against one another. The resultant direction of thecombined stream after interaction lies along the direction which is afunction of the relative momenta of the two streams.

It has been found that noise is introduced into such a system as aresult of local random variations in static pressure on the two sides ofthe stream. The random pressure variations create local pressuredifferentials across the stream which produce unwanted and uncontrolledminor deflections of the stream. Further, variations in static pressureson two sides of the stream tend to reduce the gain thereof sinceotherwise useful signal energy now appears as noise energy.

It has been proposed to equalize the static pressures on the two sidesof the power stream by undercutting one of the top and bottom walls ofthe device which walls are normally employed to confine the main streamto its plane of deflection. The prior art proposal contemplatedundercutting one of the walls in the entire region starting justdownstream of the point of interaction between the streams andterminating at the receiving apertures. The primary purpose of thisconfiguration was to defeat the effects of boundary layer lock-on whichtend to increase the gain of the unit non-linearly with deflection. Theconstruction achieved the desired result of defeating boundary layereffects. However, due to spreading of the stream which was permitted bythe undercutting of the entire region, the signal-to-noise ratio of thesystem was not appreciably increased and the gain was somewhat decreaseddue to loss of energy and pressure as the stream spread in a directiontransverse to its direction of deflection.

In accordance with the present invention, it has been found that byproviding an undercut region in one of the top or bottom walls of thedevice which has a small dimension parallel to the direction of theundeflected power stream and only a slightly larger dimension transverseto the direction of the stream, the static pressures on the two sides ofthe stream are equalized without permitting spreading of the streamtransverse to its direction of deflection. It has been found that as aresult of this construction boundary layer effects are eliminated, thestatic pressures on the two sides of the streams are main- 3,279,488Patented Oct. 18, 1966 tained substantially equal (thereby greatlyincreasing the signal-to-noise ratio of the system) and the gain of thesystem is up to five times as great as that which is obtained when theentire region between the point of interaction and the receivingapertures is undercut.

It is therefore an object of the present invention to provide a purefluid, analog amplifier having a large signal-to-noise ratio and a largegain.

It is another object of the present invention to provide an undercutregion or cross vent in one of the confining walls of an analogamplifier which cross vent has a length that is small relative to thedistance between a power nozzle and receiving apertures of the amplifierand which is only Wide enough to maintain the cross venting operationthrough the maximum design deflection of the power jet.

Still another object of the present invention is to provide a high-gain,low-noise pure fluid amplifier.

The above and still further objects, features and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed description of one specific embodiment thereof,especially when taken in conjunction with the accompanying drawing,wherein:

The single figure of the present invention illustrates a fluid amplifieremploying the cross vent of the present invention.

Referring now specifically to FIGURE 1 of the accompanying drawings, thefluid amplifier is formed as channels in a block 1 of suitable materialsuch as plastic, ceramic, metal, etc. The concept of the presentinvention is applicable to a wide variety of different types of analogamplifiers. The amplifier of FIGURE 1 is exemplary of one such designand is employed for purposes of illustration only. It is not intended tolimit, thereby, the invention to use or any specific amplifier design.The apparatus is provided with a power nozzle 2 supplied with operatingfluid through a suitable port 3 in the block 1. The power nozzle 2issues a stream of fluid into and through an interaction regiongenerally designated by the reference numeral 4. Control orifices ornozzles 6 and 7 are provided on opposite sides of the main power nozzle2, these nozzles being supplied with fluid through suitable inlet ports8 and 9, respectively.

When fluid is supplied to the power nozzle 2 in the absence of inputsignals to control nozzles 6 and 7, a stream of fluid passes through theinteraction region 4 and into a first receiving aperture 11. A rightreceiving aperture 12 and left receiving aperture 13 are also provided.The right and left sides of the interaction region 4 are opened up intoenlarged regions 14 and 16, respectively, which are vented to theatmosphere or to a suitable source of reference pressure throughenlarged apertures 17 and 18, respectively. The regions 14 and 16 andthe venting thereof through the apertures 17 and 18 is employed tosubstantially eliminate boundary layer effects between the main powerstream issued by the power nozzle 2 and the walls of the device whichdefine the interaction region 4. If walls were placed in close proximityto the stream issued by the nozzle 2, when the stream was deflectedcloser to one sidewall than the other, the stream would be moreeffective in evacuating the fluid between this stream and the closestsidewall thereby producing a further reduction in pressure on that sideof the stream. This further, and in this case unwanted, reduction inpressure would produce further deflection of the stream, the operationbeing a positive feedback operation. If the gain of the feedbackprovided were greater than one the stream would switch to the sidewalland remain attached thereto until an overriding control signal wereapplied. If the gain of the feedback arrangement were less than one thenthe stream would be deflected to an extent greater than called for bythe control signal but it would not produce complete switching. Byequalizing the static pressures on the two sides of the streams,boundary layer effects are defeated and the positive feedback phenomenais not present.

The regions 14 and 16, however, do not prevent local diiferences instatic pressure which may form immediately around the stream due tounwanted and random perturbations in the fluid system. Since theseperturbations occur at a rate which is relatively high compared wit-hsignal variations, deflections of the stream are produced which appearas noise in the output signal. To the exent that these variations occur,a portion of the energy in the stream is in the form of noise energy andin consequence, the gain of the unit is reduced.

It has been found that by undercutting a wall of the device lyingparallel to the plane of the page over a small area, the signal-to-noiseratio of the apparatus may be greatly increased and the gain of the unitincreased by up to five over that gain which is obtainable when thedevice is not so constructed. Specifically, an undercut region 19 isprovided just downstream of the region of interaction between the mainpower stream and the control streams. It is in this region justdownstream of where the streams have interacted and where there aresmall sidewalls on opposite sides of the stream, that the majordisturbances occur. The cross vent 19, illustrated in the figure, issufliciently wide to provide communication between the two sides of thestream throughout the range of deflections of the stream for which thedevice is designed. In the specific design illustrated, the length ofthe vent 19, along the axis of the nozzle 2, may be as small as of aninch and may be approximately of an inch deep. In consequence of thisconstruction, the power stream is maintained confined to its plane ofdeflection except over a very small portion of its length in theinteraction region. Therefore spreading of the stream is substantiallyprevented and no appreciable dynamic pressure of velocity drop is notedin the stream and the gain of the device is not adversely affected. Onthe other hand a substantial proportion of the noise is eliminated, andthe gain of the device is further increased.

-It is not intended to limit the use of the present invention to ananalog amplifier having the specific construction illustrated, it havingbeen found that the use of the cross vent is equally applicable tosubstantially all analog amplifiers regardless of their specificconfiguration.

While I have described and illustrated one specific embodiment of myinvention, it will be clear that variations of the details ofconstruction which are specifically illustrated and described may beresorted to without departing from the true spirit and scope of theinvention as defined in the appended claims.

-I claim:

1. A pure fluid analog amplifier comprising at least one receivingregion for a fluid stream, an interaction region, means for issuing astream of fluid through said interaction region toward said receivingregion, means for developing a differential in pressure across saidstream of fluid to deflect said stream relative to said receivingregion, a pair of walls defining opposed surfaces of said interactionregion and confining said stream to its plane of deflection asdetermined by said differential in pressure, and a cross vent formed inone of said walls, said vent having a longitudinal dimension which isshort relative to the distance between said means for issuing and saidsaid receiving region, and having a transverse dimension greater thanthe range of deflection of said stream of fluid in the region of saidcross vent.

2. I A pure fluid analog amplifier comprising at least one receivingregion for a fluid stream, an interaction region, means for issuing apower stream of fluid through said interaction region toward saidreceiving region, means for developing a control stream of fluiddirected against raid power stream of fluid to deflect said power streamrelative to said receiving region, a pair of walls defining opposedsurfaces of said interaction region and confining said power stream toits plane of deflection as determined by said control stream, and across vent formed in one of said walls downstream of the means fordeveloping a diflerential in pressure across said stream of fluid, saidvent having a longitudinal dimension which is short relative to thedistance between said means for issuing and said receiving region, andhaving a transverse dimension greater than the range of deflection ofsaid power stream of fluid in the region of said cross vent.

3. A pure fluid, analog amplifier comprising at least two fluidreceiving regions, an interaction region, means for issuing a powerstream of fluid through said interaction region toward said receivingregions, means for directing a control stream of fluid against saidpower stream in said interaction region, a top and a bottom walldefining two sides of said interaction region, said walls confining saidpower stream to its plane of deflection as determined by said controlstream, a cross vent symmetrical with respect to the undeflected powerstream and located adjacent to and downstream of the area of contactbetween said streams, said cross vent being formed in one of said wallsand having a longitudinal dimension which is short relative to thedistance between said means for directing and said receiving regions.

4. A low-noise, high-gain, pure fluid analog amplifier comprising apower nozzle for issuing a power stream of fluid, a pair of controlorifices for issuing variable control streams of fluid against oppositesides of said power stream so as to deflect said stream, at least twofluid receiving passages positioned downstream of said control orificesin intercepting relationship to said power stream, means for confiningsaid power stream to its plane of deflection as determined by saidcontrol streams, a cross vent formed in said means for confining, saidcross vent being located downstream of and symmetrical with respect tosaid power nozzle and having a longitudinal dimension which is smallrelative to the distance between said power nozzle and said receivingpassages, said cross vent having a transverse dimension greater than therange of deflection of said power stream.

5. A pure fluid analog amplifier comprising at least one receivingregion for a fluid stream, an interaction region, means for issuing astream of fluid through said interaction region toward said receivingregion, means for developing a differential in pressure across saidstream of fluid to deflect said stream relative to said receivingregion, a pair of walls defining opposed surfaces of said interactionregion and confining said stream to its plane of deflection asdetermined by said differential in pressure, and means for reducingnoise in the amplifier, said means having means for equalizing thepressures on the two sides of the stream of'fluid adjacent to anddownstream of said means for developing a difierential in pressureacross said stream of fluid wherein said means for equalizing comprisesa recess formed in one of said pair of walls, said recess having alongitudinal dimension small relative to the distance between said meansfor i:- suing and said receiving region.

References Cited by the Examiner UNITED STATES PATENTS 3,181,545 5/1965Murphy 137-s1.5 3,209,774 10/1965 Manion 137 s1.5

OTHER REFERENCES Dexter, E. M., An Analog Pure Fluid Amplifier. FluidIet Control Devices. New York, The American Society of MechanicalEngineers, 1962. Pages 4149. TI 935, S95, 1962.

M. CARY NELSON, Primary Examiner. LAVERNE D. G-EIGER, Examiner. W.CLINE, Assistant Examiner.

3. A PURE FLUID, ANALOG AMPLIFIER COMPRISING AT LEAST TWO FLUIDRECEIVING REGIONS, AN INTERACTION REGION, MEANS FOR ISSUING A POWERSTREAM OF FLUID THROUGH SAID INTERACTION REGION TOWARD SAID RECEIVINGREGIONS, MEANS FOR DIRECTING A CONTROL STREAM OF FLUID AGAINST SAIDPOWER STREAM IN SAID INTERACTION REGION, A TOP AND A BOTTOM WALLDEFINING TWO SIDES OF SAID INTERACTION REGION, SAID WALLS CONFINING SAIDPOWER STREAM TO ITS PLANE OF DEFLECTION AS DETERMINED BY SAID CONTROLSTREAM, A CROSS VENT SYMMETRICAL WITH RESPECT TO THE UNDEFLECTED POWERSTREAM